1. Field of the Invention
The present invention relates to a process for production of high purity .alpha.-(4-isobutylphenyl)propionic acid and more particularly to a process for producing high purity .alpha.-(4-isobutylphenyl)propionic acid with high reactive efficiency and at low cost by the use of a specified catalyst.
2. Description of the Related Arts
.alpha.-(4-isobutylphenyl)propionic acid has heretofore been synthesized by various methods using a wide variety of compounds as the starting material. For example, a method of synthesizing .alpha.-(4-isobutylphenyl)propionic acid using isobutylacetophenone as the starting material through five steps is known.
The above conventional method, however, fails to produce .alpha.-(4-isobutylphenyl)propionic acid at low cost on a commercial scale because (1) it uses an expensive starting material and catalyst, (2) in order to obtain a high purity product, the reaction process inevitably becomes complicated, and (3) the yield at each step is low.
In recent years, a method of synthesizing .alpha.-(4-isobutylphenyl)propionic acid or its ester by a one-step process in which p-isobutylstyrene or .alpha.-(4-isobutylphenyl)ethyl alcohol as starting material is reacted with carbon monoxide, or carbon monoxide and water or alcohol, has been proposed.
In connection with the case in that p-isobutylstyrene is used as a starting material. Japanese Patent Application Laid-Open Nos. 10545/1984 and 216849/1984 disclose methods using palladium complexes as catalyst. These methods, however, have disadvantages in that (1) it uses a catalyst of palladium which is a relatively expensive noble metal, and (2) p-isobutylstyrene is obtained by dehydration of .alpha.-(4-isobutylphenyl)ethylalcohol and since the yield at the dehydration step is not always high, p-isobutylstyrene as the starting material inevitably becomes relatively expensive. These methods have other disadvantages in that many by-products are produced and thus the yield of product is insufficient.
In connection with the case in that .alpha.-(4-isobutylphenyl)ethyl alcohol is used as a starting material, Japanese Patent Application Laid-Open No. 242642/1987 discloses a combination catalyst of rhodium and iodine, and Japanese Patent Application Laid-Open No. 263140/1987 discloses use of a mixed solvent of an hydrocarbon and an oxygen-containing organic compound.
These methods, however, have disadvantages in that (1) rhodium which is a markedly expensive noble metal is used as the catalyst, (2) .beta.-(4-isobutylphenyl)propionic acid, which is an isomer difficult to isolate, is by-produced in a considerable amount, and (3) a large amount of polymer is by-produced and thus the yield of .alpha.-(4-isobutylphenyl)propionic acid is unsatisfactorily low.
The present inventors made extensive investigations to develop a method of producing .alpha.-(4-isobutylphenyl)propionic acid using inexpensive .alpha.-(4-isobutylphenyl)ethyl alcohol as a starting material.